This invention relates generally to a nuclear reactor control system and more particularly to a device for the control of a nuclear reactor in the form of two independently controlled, concentrically assembled, reflectors.
Interest in the use of nuclear power sources for U.S. space programs has recently increased. The use of nuclear power in space has importance because spacecraft destined for deep-space exploration cannot effectively utilize solar power as an energy source due to their distance from the sun. Additionally, some satellites and planetary space probes operating close to the sun have electrical power design requirements that cannot withstand cyclical solar exposures or rely on rechargeable batteries. Furthermore, as the electrical power requirements for spacecraft increase, the capability of solar power to supply the electricity becomes limited by the sheer size of solar panels. Therefore, a reliable, long term supply of energy is needed in a low-mass form that requires minimal space. Nuclear power can supply this energy need.
There are two types nuclear power sources used in space applications. One type, called radioisotope thermoelectric generators (RTGs), uses the decay of naturally radioactive elements to produce heat. The other type of nuclear power source uses nuclear reactors to produce heat. Space nuclear reactors employ several power conversion technologies. Among them are thermoelectrics and thermionics. In general, the thermoelectric nuclear reactor uses a circulating medium to transport heat from the reactor core to energy conversion devices located behind a radiation shield. In one reactor, the SP-100, a liquid metal (Li) is used in a pumped loop to transport the core heat to the conversion devices. The thermionic nuclear reactor concepts generally perform the energy conversion in the core and transport the waste heat via heat pipes or liquid metal loops.
To achieve a maximum level of system reliability and redundancy in conventional reflector control systems employed in test reactors, like the Advanced Test Reactor (ATR) at the Idaho National Engineering Laboratory (INEL), or the SNAP and SP-100 space reactors, multiple and independently operated and controlled reflector elements are required. In the ATR, SNAP, and the Russian TOPAZ reactors, reflector drums are utilized around the perimeter of the core. In the SP-100 reactor, hinged "shutter" reflector segments are employed. In both of these systems, failure of one or more of the reflector drives or control systems may disable the reactor startup or shutdown, and at a minimum, will compromise full mission capability.
A new space nuclear power concept has been developed by the INEL. This concept, the Small Ex-core Heat Pipe Thermionic Reactor (SEHPTR), has unique features and significant advantages for both defense and civilian space missions. SEHPTR was developed to meet needs for space nuclear power in the range of 10 to 40 kilowatts. In addition, other requirements that space nuclear power systems must meet to be acceptable to potential users have been identified. These requirements include safety of the system during launch and operation, and the ability to perform rigorous ground testing. Performance requirements dictate a high reliability and emphasize reduced system volume and mass. Additionally, several spacecraft developers have indicated a reluctance to incorporate into their spacecraft any primary power subsystem that has potential mission ending single point failures.
It is therefore an object of the present invention to provide a reactor control device for a primary nuclear power subsystem which is subcritical in launch accident scenarios, and which eliminates credible mission ending single point failures.
A further object of the present invention is to provide a reactor control device in which either of two reflectors are capable of independently controlling the reactor to provide redundancy.
Yet another object of the present invention is to provide reliable reactor control for a space nuclear power system with a minimum of redundant hardware and minimum mass penalty.